Several known collet chucks for gripping workpieces at machine tools, particularly at lathes, are provided with three or more chuck jaws which are placed against circular cylindrical chucking bolts. The chucking bolts are each carried longitudinally displaceable to the chuck body in a circular cylindrical guide hole, the longitudinal axis of which is inclined from the free end face of the chuck towards the rear end of the chuck so as to be inclined with respect to the longitudinal axis of the chuck. The chucking bolts are actuated via a common draw-in disk or a common draw-in ring which is coupled to the draw-in device of the machine tool via a chucking tube.
These chucking bolts always have the same contact against the wall of their circular cylindrical guide hole in any axial position, that is, with any chucking diameter of the workpiece. However, since they must necessarily have only a very small dimension in the circumferential direction, the projected contact surface in the guide hole is comparatively small. In addition, the gripping surface for the workpieces has a comparatively small circumferential extent because it can only be constructed by flattening the circular cylindrical chucking bolt.
These collet chucks also have the disadvantage that the chucking bolts are almost completely surrounded by the chuck body. For this reason, the chuck body must have a comparatively large radial dimension. For any given outside diameter, the collet chuck has only a comparatively small centerhole size or, conversely, the chuck has a comparatively large outside diameter for a given centerhole size.